FIGHTING NUTRIENT LOSS. Iowa farmer Tim Smith, strip-tills half corn and half soybeans on about 500 acres of his 800 acres near Eagle Grove. For the past 4 years, he’s been participating in the Mississippi River Basin Initiative. The program incentivizes strip-tillage, cover crops, bioreactors and nutrient management to reduce the amounts of nitrates that end up in the Mississippi River and ultimately the Gulf of Mexico. Photo courtesy of Tim Smith

Tim Smith has been strip-tilling half corn half soybeans on about 500 of the 800 acres he farms near Eagle Grove, Iowa, for the past 4 years. Smith, who used ridge-till and conventional tillage practices in the past, was inspired by a nearby farmer who’d been strip-tilling for 8 years to pursue the strategy. Opportunity met interest when the NRCS introduced their Mississippi River Basin Initiative (MRBI) to his watershed.

The MRBI program included cover crops, nutrient management, introducing a bioreactor and strip-tilling. It’s designed to reduce nutrient loads that filter into the streams that lead to the Mississippi and ultimately to the Gulf of Mexico.

Smith says that of the four elements included in the MRBI program, strip-till has helped improve soil conservation, nutrient placement and time and equipment savings. When it comes to quantifying his return on his strip-till investment, the biggest boon has come in the form of losing less topsoil.

Smith says he adopted the practice at the perfect time, because weather conditions on his farm during the last few years would have battered his acreage if he stuck with 100% conventional tillage practices.

“The biggest return with strip-till is greatly reduced loss,” says Smith. “My soil has held up better in adverse conditions. With the excessive rains we’ve had over the last few years, having more residue on top of the soil helps to preserve that soil structure and improve water infiltration. ”

Building the Right Equipment Mix

Incentives offered by the MRBI allowed Smith to get new equipment, and retrofit old equipment he had left over from ridge-tilling. He uses a 3-point 8-row DMI toolbar on 30-inch spacings to build his strips.

“I added row cleaners onto it and I changed it to mole knives and sealers,” says Smith. “The 20-inch notch blades float to help build the berm. There’s a hitch on the back that I use to pull my Concord air cart.

“It’s pretty simple. I know a lot of the strip-till machines are long and have lots of clearance, but everything on mine is pretty tight.”

Smith also uses auto-steer and GPS on his John Deere 16-row planter and strip-till rig, opting for Trimble’s satellite-based RTX signal.

Seeing the Soil Health Benefits

Being in an area with erosion issues, one of Smith’s main concerns is protecting his soil. But during his 4 years of strip-tilling, he’s not only seen improved water retention, but a substantial increase in soil health and structure as well.

“The first year of strip-tilling, I took my spade out and dug out pieces of the field,” says Smith. “I brought up 6-8 inches off the top and it just crumbled in my fingers. The soil structure starting improving quickly and it’s not loose, fine soil that drifts through my fingers and easily erodes.”

He’s also seen a return of the earthworm population, long absent from his conventionally-tilled acreage. This has helped significantly with residue management and decomposition.

“I can go out and kick just about any piece of residue and there are bound to be worms under it,” says Smith. “NRCS did some counts and said there were about 12-18 worms per cubic foot. I guess I can get better than that, but when I did full tillage I’d have difficulty finding any.

“Now, they’re going up and down the soil profile and taking the residue down deeper, and processing it. It’s a definite improvement there.”  

Nutrient Placement and Retention

Introducing cover crops, strip-till and a bioreactor has been an exercise in tracking the nutrient cycle for Smith. A bioreactor, which is essentially a buried trench filled with wood chips through which tile water is allowed to flow, uses the microorganisms that colonize it to convert nitrates to nitrogen gas as they pass through. Smith would like to see as little fertilizer as possible leech away, and have better control over what he applies.

Rolling Back Application

ROLLING BACK APPLICATION. Soil testing has shown Smith that his P&K levels in the strips are in the optimum range, enabling him to cut application rates by as much as 25%. He uses a one-pass system in the fall to build his strips with an 8-row DMI toolbar on 30-inch spacings.

Photo courtesy of Tim Smith

To reach this goal, Smith is employing a combination of strategies. Soil Testing and tile water sampling consistent with the initiative program has shown Smith that the bioreactor and cover crops have helped with nitrate loss.

“I sampled the water flowing into the bioreactor and then the outflow to see what sort of reduction took place,” says Smith. “The level of nitrates in my tile water surprised me because I thought that I was putting nitrogen on in a safe way. When I applied it in the fall in the past, I would use N-Serve nitrogen stabilizer and wait until the soil temperatures were in the low 40s.”

Despite these precautions, the soil tests showed that the nitrate levels flowing to the bioreactor in the tile water were well above the EPA’s safe water level of 10 parts per million. However, the tests did show that the reactor was able to bring those rates down to a much more comfortable 2-3 parts per million on the output side. Biomass samplings of his cereal rye cover crops showed that he was able to retain a substantial amount of nitrogen in the field before it reached the tile water.

“I think the cover crops are one of the best tools we have to reduce nitrate loss,” says Smith. “The biomass samples we took showed 30 pounds of nitrogen in the cereal rye which didn’t go down my tile lines.

Smith says he’s not sure if there’s been enough research done to determine when exactly that nitrogen is available, but it’s there at some level and if anything, it’s not leaving the farm immediately.

Complete System

While Smith’s bioreactor and cover crops work together to prevent nutrient loss on the backend, strip-till has given him added control over placement. Smith uses a single-pass system in the fall to build his strips, and he’s gotten away from applying nitrogen then, in favor of doing it in the spring.  

Slowing the Flow

SLOWING THE FLOW. As part of the Mississippi River Basin Initiative Smith is participating in, he had a 110-foot long, 10-foot wide and 5-foot deep wood chip bioreactor installed on his property. A bioreactor, which is essentially a buried trench filled with wood chips through which tile water is allowed to flow, uses the microorganisms that colonize it to break down nitrates as they pass through.

Photo courtesy of Tim Smith

He bands phosphorous and potassium in an 8-inch wide and 8-inch deep strip in the fall through his strip-till rig and a Concord air cart pulled behind. After sampling, Smith has been confident enough with his P&K placement and range that he’s been able to dial the rates back about 25%.

“I need to be confident with my levels before making any serious adjustments,” says Smith. “My P&K are in the optimum range and it really doesn’t pay to put on much more fertilizer.”

Smith credits the reduction to being able to place the band so close to the root zone with strip-tillage.

He’s reduced application to about 100 pounds per acre of diammonium phosphate (18-46-0) and 150 pounds per acre of potash (0-0-62).

He hasn’t reduced nitrogen rates yet and applies 120 pounds of nitrogen as anhydrous ammonia in the spring, ahead of planting.

“I have used 32% at sidedress before, but it just depends on how the spring goes,” Smith says. “If I can get it on, I’ll put it on. But if it’s too wet in the spring, then I’ll just sidedress it later.”

Further experiments with nutrient management may eventually develop a scenario in which he can think about reduced nitrogen rates. But for now, Smith is focused on keeping what he applies on his farm and out of the nearby waterways.